Method and apparatus for pulse production in particle accelerators



Dec. 13, 1966 L. MORGAN ET AL METHOD AND APPARATUS FOR PULSE PRODUCTION IN PARTICLE ACCELERATORS Filed April 2, 1962 Unite States Patent 3,291,993 Patented Dec. 13, 1966 ice 3,291,993 METHOD AND APPARATUS FOR PULSE PRODUC- TION IN PARTICLE ACCELERATORS Ira L. Morgan and John R. Porter, Austin, Tex., assignors to Texas Nuclear Corporation, Austin, Tex., a corporation of Texas Filed Apr. 2, 1962, Ser. No. 184,174 16 Claims. (Cl. Z50-214) over a wide range of values in a relatively simple and inexpensive fashion.

The invention is of particular utility, and is herein described, in association with` a neutron generator of the type in which a positive ion beam is lproduced in a region at a high positive potential with respect to ground (this high-voltage region being the so-called terminal portion of the system) and being employed, after acceleration due to the potential drop, for the bombardment of a target productive of neutrons in response to such bombardment. Pulsed operation of such generators, producing neutron bursts of high intensity, normally periodically repeated at more or less rapid intervals, and with various durations of ion beam pulses, are well-known for a variety of purposes. Such pulsed operation has the advantage not only of permitting instantaneous bombardments of the target with intensities which would rapidly destroy the target if continuous, but also per-mits the employment of such generators for, for example, neutron bombardment of materials for analysis and similar purposes wherein the activities Iproduced by the neutrons, and used for identification, may be of extremely short half-life; furthermore, even where continuous operation is not prohibitive for reasons such as target life or the type of measurement involved, such pulsing is frequently employed as a convenient means for controlling overall rate of neutron production per unit time without disturbing the ion source parameters once this portion of the terminal system has been tuned, so to speak, for optimum, i.e., maximum, performance.

Special-purpose accelerators are frequently constructed for such pulsed operation with the frequency and duration of the pulses selected for the particular intended purpose. A pulse generator of more or less conventional design is self-contained in the terminal system, with the ground or reference potential normally employed in electronic circuits being the conducting portions of the housing, etc., of the terminal structure, frequently called terminal ground, the entire terminal being, of course, fully insulated from actual earth ground except for interposition between earth ground and terminal ground of the device producing and sustaining the high potential difference, of which there are many variations, the most popular for reasons of economy being the type characterized as the Cockroft-Walton, commercially made by -a number of manufacturers.

Although such special-purpose pulsing systems as just described are in general suitable for the purposes for which they are designed, their market is largely limited to single-use purchasers. To increase the utility of such systems, they have been built with pulse generators of variable frequency and pulse duration incorporated in the terminal system, and neutron generators of this construction are in fairly Wide use in laboratories and similar installations, adaptation of the frequency and duration desirable for various uses either being made during complete shut-down of the generator, i.e. with the terminal system dis-charged, or by means of relatively clumsy long insulating rods. Because of the mechanical problems associated with the latter type of control, the use of calibrated continuous controls of the type which are commonplace in pulse generators designed for general utility purposes for the control of frequency and duration are unreliable for the purpose of establishing known and reproducible pulse repetition and duration rates; the precision lcalibrated dials and similar indicators normally capable of .permitting settings of these variables with high accuracy become useless for precision setting of potentiometers or similar control elements to which the motion must be imparted by means of a coupling comprising a rod of, for example, nylon or polystyrene many feet long, even when the clumsiness of making such rods of suicient diameter to be reasonably rigid against torsion is permissible. Accordingly, although control of frequency and duration was, prior to the present invention, considered the most pra-cti-cal type of control for commercial generators designed to be more or less universal in utility, these practical limitations have in general restricted this type of manual control of the pulsing occurring in the terminal system 'to be limited to stepped, rather than continuous, control, the assur-ance of accuracy of setting given by the indexing mechanism of a switch operable to adjust the frequency or duration in discrete steps overbalancing by far the loss of the advantages of continuous control.

Even in such switched systems, however, the problem of reading of the switch position at the remote end of the operating rod greatly limits the resolution of the adjustment; i.e., the smallness of the steps by which such variations may be accomplished is seriously limited. The employment of a rotary switch with a large number of positions requires, in order that the shaft position be readable at the remote end of the shaft of such materials as are required for insulation, that the shaft be of large diameter. Control over a wide range in small steps requires such a large number of series-connected switches as to be not only extremely inconvenient but enormously expensive because of the large number of precision resistors and similar components required for producing reliable and reproducible accurate settings with such a system. Accordingly, the universal adjustability of practical and economical control constructions has long been of a true universality far from that obtainable with many kinds of variable pulse generators commonly employed for -other purposes where such problems are not encountered, all such switching systems in reasonably widespread use employing such gross steps as to confine adjustment of frequency and duration largely to orders of magnitude, rather than to precision settings of such a resolution as to approach anything resembling continuous adjustment. Furthermore, even in such crudely adjustable systems, the cost of even a relatively small number of the separate impedance elements required for the wiring of such switches, particularly when coupled with the wiring operation itself, has rendered the overall cost of the pulse generator incorporated in the terminal system far higher than the cost of an ordinary pulse generator employing continuous controls, despite the vast inferiority of perform-ance as regards continuity of adjustment. It will be seen that in addition to the problems superimposed by the long rod control shafts, the comparison of pulse generator types as regards adjustability is similar to that in any other choice of pulse-generator design, as between step-wise and continuous control, the advantages of the latter from all standpoints for any pulse generator of application approaching universality having long since' been demonstrated by the virtual disappearance of switches as sole control elements in pulse and similar types of signal-producing equipment caused by the relatively low cost of precision potentiometers and associated calibration dials and similar components for continuous adjustment which are common knowledge.

The unsatisfactoriness of available types of controls suitable for operation Without shut-down of the accelerator has led to a number of attempts to produce the desired pulse adjustments in other manners. A Well-known general type of substitute for mechanical adjustment from remote locations is the type of remote control in which linkage between the point of control and the controlled operation is made by non-mechanical means. Obviously, the nature of the problem permits no conductive connection between the terminal system and the surrounding region, so some form of radiation link could provide the solution. Attempts along this line have heretofore been made for many years, but all have had defects and disadvantages rendering them either completely unsuitable for commercial accelerators or usable only under very restrictedy conditions. For example, it has been attempted to contr-ol the pulsing remotely by radio-frequency linkage, employing a small transmitter and receiver. Such attempts to solve the problem have failed to deal in any satisfactory fashion with the broad-spectrum electrical noise and hash inherently present in the terminal system, the transmitter power required to produce any reasonable signal-to-noise ratio being almost completely prohibitive for wide commercial use. Light transmission is another type of non-conductive link which has heretofore been attempted, but never in such a manner as to produce satisfactory results. One accelerator reported in the literature, for example, employs a pulsed light source with the light pulses detected in the terminal system and employed to drive stepping switches, thus producing a noncontinuous type of adjustment, but one which is capable of adjustment rapidly and in reasonably small steps over a very wide range, the type of switches used in automatic telephony being capable of pulse-actuated switching over many positions in very simple fashion. However, when the cost of the precision resistors required for use with such switches in the present type of .application is considered along with the cost of wiring such a system, this type of control again becomes' obviously unsuitable for a commercial generator, particularly for one of the relatively low cost typied by the Cockroft-Walton neutron generator.

There has thus been to date no really satisfactory method or apparatus for varying the pulsing frequency and duration over a wide range of values, suitable for widespread use of such generators as general-purpose devices for diverse uses in laboratories and other places in which a wide range of requirements may be encountered, even for switch-type, i.e., step, adjustments, let alone for the continuous type of adjustment. It is the principal object of the present invention to provide a fully satisfactory universal pulse control, and particularly such a control in which both the frequency and the pulse duration of the pulsing of the beam are continuously variable while the accelerator is in full operation.

In considering possible solutions to the problem of devising a satisfactory control, it is first necessary to understand and analyze why obvious methods and apparatus which are more or less conventional in control problems which superiicially appear to be the same, but whose lack of success in solving the present problem requiring resort to such complex systems as the driving of stepping switches by light pulses described above, are unsatisfactory. As previously indicated, the transmittal and reception of a radio-frequency `pulse and production of a suitable square-wave pulse during its duration to operate the beam, thus permitting the use of conventional continuously variable pulsing equip-ment at earth ground, has never been successful up till n-ow :because of inadequate signal-to-noise ratio obtainable at the transmission powers which can be produced with any reasonable economy. Superficially, it would appear that an enclosed light system, such as reported in the literature as rnentioned above, could be adapted for the present purpose by transmitting and detecting light pulses whose duration and freqency would lbe reproduced in an electrical signal which could be employed as the operating pulse in the terminal system, thus permitting control by simple variation of the pulses delivered to the light source. This idea, although simple in principle, proves to be completely impractical for the present purposes. For reasonably universal use, i.e., to cover the ranges which are desired in such a device, the pulse widths required range all the way from approximately a microsecond to a substantial fractional portion of a second, with a range of frequencies such as to produce operation of the beam, with such pulse durations, over a range extending from a very minute portion of the total operation time up to a very large portion, in which the beam is in operation a substantial fraction of the time, i.e., the pulse duration is a substantial portion of the repetition interval. The frequency of repetition in itself, i.e., when not related to the pulse duration, creates no substantial problem in such a postulated control system. However, when the pulse duration is considered, particularly along with other factors present, the impracticality of such a system can be seen. First of all, although the entire light transmission system, including the source and the detector, can be enclosed to exclude the ambient light which constitutes the noise, in a rather simple manner, the electrical signal output of the detector again encounters the electrical noise problem, against which protection is much more diflicult, so that attempts to use small-signal detector output followed by suitable amplification fail with any degree of electrical shielding which can practically be achieved. Accordingly, the light output of the source and the sensitivity of the detector must be such as to produce large signal detector output to produce satisfactory discrimination against the electrical noise present in the terminal system. The requirement that the system be capable of producing overall on-time representing a substantial fraction of the olf-time, coupled with the requirement that the system be capable of relatively long pulse durations, combine to make this apparently simple type of system completely impractical, andl at the other end of the scale, the requirement of production of extremely short pulses, such as those of a microsecond duration, likewise cannot be obtained. It is extremely diliicult to obtain or devise a light source, particularly a light source of great brilliance, producing anything approaching the desirable range of pulse Widths, either in response to applied square-wave pulses at the electrodes or otherwise. As regards the detector, the highoutput requirement indicates the necessity of the use of high-gain photomultipliers, and su'chy `devices are not capable of operation for'the long periods of life required in components for such systems with any large fraction of on-time in which they are exposed to the illumination producing the high-output voltages discussed. Further, it is found that the .response time of thesehighly sensitive detectors is far too long for the reproduction of light pulses of, say, a microsecond duration. Similar practical problems are encountered in adapting to the present problem solutions of other types which have been used in the performance of tasks which look analogous, but only deceptively so.

The present invention provides a control system using, like the type of light system (or radio-frequency pulse system) found to be unsatisfactory, a conventional type of variable pulse generator at 4earth ground, with the continuous controls readily available in such types of equipment as sold commercially, but uses a different type of readily available pulse generator, and, concomitantly, employs the transmitted pulses for production of the desired pulses in the terminal system in an entirely different manner from any heretofore described. Although elements of the present system have heretofore been used for purposes supercially similar, it will be found that the combination of these elements in the present system produces an overall system which successfully avoids all of the problems and faults in prior systems, to produce a method and apparatus fully achieving all of the purposes discussed above.

As will be seen from the description of the particular embodiment of the invention illustrated in the drawing, to be described below, the system has a number of novel aspects contributing to the overall desirable operation, some of which may be optionally omitted for certain uses, and some of which can be replaced by equivalent steps and structures without substantial departure from the basic elements of the invention. Both the general and the detailed aspects of the method and apparatus of the invention will 4best be understood from a description of the particular embodiment shown in the drawing.

The single ligure of the drawing shows in schematic form a system incorporating the invention.

In the e-mbodiment shown in the drawing, `a pulse generator provided with continuously variable controls shown in schematic form at 12 and 14 is used `for the control, being at any reasonable distance lfrom the terminal system generally designated 16, consisting of all of the parts and components mounted in the high-voltage portion of the overall system, this portion of the system being housed in a type of housing conventional for the purpose (not illustrated) and having the metallic portions of the housing, the electronic chassis in this terminal portion, etc., mutually interconnected to form the usual terminal ground, indicated by the chassis ground symbol at 18, as distinguished from the earth ground 20. A high voltage supply 22 is shown as fbeing connected between earth ground 20 a-nd terminal ground 18, it being understood that this supply 22 is merely la schematic indication of the existence of the high potential dierence, whether produced by, for example, a Cockroft-Walton system or a Van de Graai or by any other device Ifor production of the high terminal volta-ge. It will be understood, of course, that the term hi-gh voltage `as herein used in connection with utilization of the invention refers to voltages of the order of many thousands of volts, normally at least 50,000 volts or higher with respect to earth ground, thus creating the problem solved by the present invention, which is entirely different from the types of problems encountered in equipment in which pulse transmission and production systems in some respects .supercially resembling those here employe-d may have heretofore been used. It will also be understood that although in t-he system illustrated, wherein the terminal system is that of a positive ion accelerator with an ion source 424 in the terminal portion and a target 26 substantially at earth ground, the terminal is at a positive potential, the polarity is lnot of ygreat consequence as regards the basic teachings of the invention.

Before proceeding with the description of the present invention, the accelerator :may be lfurther briefly described to illustrate the utilization of the pulses produced in the terminal in the present instance, alhough it will be obvious, after understanding of the invention, that its application is not limited to the voltage pulses here employed for ion beam control, b-ut can be used for pulse operation of any other electrical parameter, such as a current, a trequen-cy, etc., where such a parameter is to be varied in the terminal system from earth ground. In the highly schematic illustration of the drawing, the positive ions, formed in a beam by a suitable device for this purpose shown at 28, are passed through a lens 30 at a very early sta'ge of their acceleration. rllhe beam on the target 26 is interrupted (-or, alternatively, produced, depending upon the design details) by the impressment between detlection plates 32 of periodic square pulses 34, deflecting the beam from (or to) the sl-it in the lens 30. The pulses 34 are produced at the output of abuffer and amplifier 36 in response to corresponding square pulses 38 at its input. This part of the terminal ,system is conventional and will not be further described herein, being merely an instance off the utilization of the pulses 38 of variable frequency and duration produced by the :generation and transmission system of the invention in the high-voltage terminal.

The pulse generator 10, as indicated above, although of a .type readily available commercially, is, unlike the type of `generato-rs used in unsatisfactory systems described above, not designed for the production of pulses corresponding in duration to the ultimate pulses to be produced and utilized in the terminal system, although their frequency is the same. In the present system, the pulse generator 10 produces pulses of identical duration at all frequencies and irrespective of the lpulse duration to be ultimately produced. The lultimate pulse durati-on is represented at the output of the generator 10 by the delay period between the periodic pulses 40 produced on one output line 42, constituting the initiating pulses, and the pulses 44 produced on the other -output line 46, identical except as regards the delay, constituting the terminating pulses. Pulse generators of this type are well-known in a variety of details of construction, and are commercially available under such descriptive designations as dual time-delay generators and similar designations, being used for a variety of purposes requiring separate outputs of periodic pulses substantially identical except as regards the delay, both the delay time Vbeing continuously variable over a wide range by the control 12 and the frequency being similarly variable over a wide range by the control 14. It will of course be understood that the controls 12 and 14 are illustrated highly schematically, the actual commer-cial constructions including range switches, line and coarse controls, calibrating devices, etc.; it will also be readily obvious to those skilled in the art that the ampliers required to be inserted in the respective lines to make the pulses 40 and 44 of sutlicient power to drive the li-ght generation `systems are omitted `from the drawing, being considered as included in the ygenerator 10 schematically illustrated, although in actual commercial practice such amplitiers are separate units, the required design for present purposes being well-known. The output lines 42 and 46 are respectively coupled to light sources 48 and 49, a desirable type of source Ibein-g a high-intensity neon glow tube such as the Sylvania R1l66. The pulses produced at the outputs of the ygenerator 10 are of the order of a fraction of a microsecond, and the light pulses produced by such a source are only very ,slightly longer. The light pulses are conducted through insulating opaque tubes 50 and 52, normally of the order of 6 to l0 -feet in length in the case of a terminal at a potential in the neighborhood of to 15() kv. Sensitive photomultiplie-rs 54 and 56 in the terminal system detect the pulses to produce output electrical pulses 58 and titl. As previously indicated, these sensitive photomultipliers, such as the 931A, when connecte-d for high output do not have a sufliciently fast response time to follow the rapid rise and decay of the actual light `pulses, and the electrical pulses accordingly emerge with mu-ch greater width, a rise time of one microsecond and a decay time of three microseconds being fairly typical. These pulses are fed through pulse .shorteners 62 and 64, such as differentiating circuits or delayline clippers, to produce shorter pulses 66 and 68, for example of a total duration of approximately a hallf microsecond. It might be noted at this point that the vertical dotted lines, representing the time of occurrence of the pulses in the drawing for purposes of illustrating the constancy of the delay throughout the matched systems described, are drawn in all cases through the peaks of the pulses for simplicity of illustration and comparison of pulse shapes. Actually, it will be obvious that these pairs of vertical lines do not represent identical times throughout the system (even after allowance for transmission time, etc), since it is obvious, for example, that the pulse S does not commence earlier than the pulse 40 by which it is generated; the showing of these time lines as drawn through the maximum value of each pulse, rather than representing identical times, is advantageous in ready observance of the pulse forms, and has no effect on the illustrated constancy of delay.

The outputs of the pulse shorteners 62 and 64 are fed to a dual-input bistable multivibrator or trigger pair 70 of the type having balanced inputs, the input to which initiating pulses 66 are fed being responsive to these pulses to initiate output pulses 38, and the input to which the pulses 68 are fed being responsive to these pulses to terminate the pulses 38.

The particular system illustrated being understood, the overall nature of the operation, and the lbroader aspects of the invention, will become apparent. It will be understood that the light sources 48 and 49 and the photomultipliers 54 and 56 are contained in suitable opaque enclosures (not illustrated) opening only on their respective light guides 50 and 52, so that the two light-transmission paths are completely isolated from each other and also from ambient light. In principle, if ambient light were to constitute no problem, it would only be necessary to isolate the two paths `from each other to accomplish in full all of the purposes of the invention, which may, even in its narrower aspects, be performed by any manner of assuring that light pulses of one channel do not produce substantial .response in the detector of the other channel. For example, it is within the teachings of the invention in its broader aspects to employ structures less advantageous from the standpoint of simplicity and economy, such as polarizing lters mutually isolating the light channels. in ultimate effect, even though a single common physical path be employed to exclude ambient light, and indeed enclosure against ambient light may be dispensed with altogether in some uses of the invention in which ambient light becomes negligible either because of conditions dictating that operation will in any event be in substantial ambient darkness, or because the light sources employed are of higher intensity than those here described. Where exclusion from ambient light constitutes no problem, appropriate isolation of the two channels may be obtained by simple lens systems if so desired.

The purpose of the pulse shorteners 62 and 64 may readily be understood upon the pointing out that the system is designed for the production of pulses of the order of one microsecond or less in duration, sometimes shorter than the rise time of the pulses at the output of the multipliers. Under these conditions, if the pulse shorteners 62 and 64 were omitted, any slight change in the sensitivity of one of the inputs to the multivibrator 70, or of original pulse size in one channel or any other slight asymmetry developing in the system would produceA such a large change in the trip point of the multivibrator, ie. in the time of its actuation by the leading edge of the pulse 58 or 60, that the highly accurate calibration of the delay control 12 would lose its value in assuring exact length of the pulses 38 and the pulses 34 eventually utilized. The shortening of the pulses to the form shown at 66 and 68 eliminates this source of error.

The purpose of the isolation of the two channels is related to the large amount of electrical noise inherently present in the terminal, particularly in accelerators of the type illustrated. Were it not for this factor, the broader teachings of the invention might be employed by employing a common channel for both the initiating and the terminating pulses, since multivibrators of generally similar gross operation to the type with dual inputs each responsive only for switching in one direction are available and well-known with a single input, acting as a switch which alternates its condition with each input pulse, i.e., the type of circuit commonly known as a scale-of-Z. The basic difficulty with such an adaptation of the broad method and apparatus is the certainty that unless there were provided an amount of shielding which is essentially prohibitive, if possible at all, there would occasionally occur a surge or spike in the ever-present hash which would insert an extra reversal of condition of the switch so constituted, thus turning on-time to off-time, with consequence in the accelerator operation which would be likely to be disastrous. Accordingly, the use of the dualinput switch as described is highly essential in the present utilization, although there may be systems in which the single-input type of switch may be employed.

This description of the purpose of the isolation leads,

' of course, to other variations which may be employed,

although not as desirable as the present construction for the purpose illustrated. For example, a single light channel, i.e., a single source and a single detector, may be utilized in certain applications, with the pulses 40 and 44 distinguished by some feature such as modulation or shape, with the detector output fed to opposite inputs of the two-input switch through suitable lters or other distinguishing means assuring the rsponse of the respective inputs to the switch only to the initiating or terminating pulses, as the case may be. Also, in view of what has been said, it will be obvious that the pulse shorteners 62 vand 64 may be eliminated in applications of the invention `ditfering substantially from the one illustrated.

In addition to solving the problems heretofore believed to be unavoidable by providing a light-transmission method and apparatus, the pulse formation of the invention may be applied to other types of links or transmissions in the present type of system. For example, it will be seen that if the initiating and terminating pulses are transmitted in, say, a radio-frequency system, the fact that they are always identical in shape, and thus always have exactly the same frequency components, irrespective of changes in ultimate pulse lduration by factors as great as 100,000, permits the use of special-shaped pulses, which may be employed for improved noise-discrimination, and the short on-times of the transmitted pulses make it possible to ernploy relatively powerful pulses without excessively powerful transmission equipment. Indeed, even supersonic transmission may be employed in particular cases.

It might be noted that the advantages of the system illustrated and described over -prior pulse-control methods and apparatus employing light links are even greater than previously described. As earlier indicated, the best such system thus far devised uses the output of the photomultiplier to operate a series of stepping switches. In the event of the occurrence of a .surge or spike of great amplitude, unless an extremely large amount of shielding were used, the stepping switch would be advanced by the simulation of the multiplier output pulse and would remain in the same condition thereafter, i.e., advanced one position beyond its desired position, any such further additions being cumulative. ln the present system, however, such an occasional surge of pickup, simulating an input pulse, is inconsequential in effect, since its effect is immediately erased by the next succeeding pulse pairl It will also be observed that by shutting o the pulses -in one of the channels, the ion beam may be maintained in either an on or olf condition, any reversal by a noise spike being immediately corrected. Thus the present system has still further advantage beyond the factors of simplicity of operation and relative cost for comparable performance of the use of a pulse generator at earth ground with continously variable controls for the frequency and duration of the pulse produced in the terminal system.

Certain modifications of the illustrated embodiment of the invention which may be made while remaining within the teachings of the invention are discussed above. Many other ways of utilizing the method and apparatus of the invention will readily occur to those skilled -in the art, some being immediately obvious, and some being seen only after study. The fact that the method of the invention is not necessarily confined to any particular apparatus may be understood from considering a type of practice which, although trivial in importance as :a practical matter, is illustrative of the fact that portions of the apparatus may, -as regards the basic -or elementary teachings of the method -aspect of the invention, be practiced by manual operations. For example, it will readily be obvious that theoretically (and possibly even practically, for certain purposes) the pulse production illustrated as being performed by the pulse generator could be performed manually by the opening and closing of switches.

In view of the foregoing, it will be clear that the scope of the protection to be afforded the invention should n-ot be limited to the particular embodiment shown in the drawing, but should extend to the method and apparatus as `described in any of the appended claims, and equivalents thereof.

What is claimed is:

1. In the operation 4of a charged-particle accelerator or the like including -a terminal portion at a high voltage with respect to its surroundings, the method of producing electrical pulses of variable yduration and frequency in such termin-al portion comprising generating, in a region substantially spaced from the thermal portion, periodic pulse pairs comprising initiating light pulses and terminatin-g light pulses delayed with respect to the initiating pulses, detecting such pulses in the terminal portion, altering and restoring an electrical parameter in the terminal portion in response to successive pulses thus detected and Varying the delay between the pulses of the pairs independently of their frequency.

2. The method of claim 1 characterized by mutually isolating the detected initiating and terminating pulses in dilerent channels and switching the parameter in only one `direction in response to each channel, so that any accidental phase reversal is immediately corrected.

3. The method of claim 1 characterized by shortening the initiating and terminating pulses after detection, so that the duration of the pulses so initiated and terminated yremains in accurate correspondence with the period of delay even at durations shorter than the pulse width prod-uced on detections of each initiating and .terminating pulse.

4. Apparatus for charged-particle acceleration `and analogous purposes comprising .a high-voltage terminal system insulated from its surroundings, 4light-p-ulse-generating means insulatedly spaced from the terminal system for producing periodic light-pulse pairs lof manually varia- =ble time delay, light-detecting means in the terminal system, and a switch in the terminal system, operable in response to successive light pulses so detected to altern-ate an electrical parameter in the terminal between two conditions.

5. Apparatus as set forth in claim 4 having a pulseshortener interposed between the light-detecting means and the switch.

6. Apparatus as set forth in claim 4 wherein the switch has two inputs, each operative to actuate the switch in only one direction, and detection of only one member of each pair of pulses being transmitted to each input.

I7. Apparatus as set forth in claim 6 wherein the li-ghtdetecting means comprises two mutually isolated detectors, each coupled to one input.

8. Apparatus as set forth in claim 6 wherein the lightpulse-generating means comprises two light sources and means to produce one pulse of each pair in each' source.

9. Apparatus for charged-particle acceleration and analogous purposes comprising a high-voltage terminal system insulated from its surroundings, pulse-'generating means for producing in separate channels periodic initiating and terminating pulses, mutually isolated light sources connected to each of said channels, mutually isolated lightdetectors in the terminal portion, means dening a lighttransmission path between the sources and the detectors including means for conning the response of each detector to the pulses from one source, and a switch in the terminal system having two inputs each adapted to reverse the condition of the switch in one ldirection only, each light-detector being couple-d t-o one input.

10. The apparatus of claim 9 wherein the means for confining the response of each detector to the pulses from one source comprises means for mutually isolating the light path from the respective sources to the respective detectors.

11. The apparatus of claim 9 wherein the light-transmission path-dening means includes at least one insulating opaque enclos-ure excluding ambient light.

12. The apparatus of claim 9 wherein the light-transmission path-dening means comprises a pair of opaque tubular enclosures each connecting a light source with the corresponding detector.

13. The apparatus of claim 9 wherein the coupling of each detector to its corresponding switch input includes a pulse shortener.

14. Apparatus for charged-particle acceleration and analogous purposes comprising a high-voltage terminal system insulated from its surroundings, pulse-generating means for producing in sepa-r-ate channels periodic initiating .and terminating pulses, mutually isolated light sources connected to each of said channels, mutually isolated light-detectors in the terminal portion, an opaque tubular enclosure conducting light from each source to each detector, a pu'lse-shortener connected to each detector output, and a bistable generator having balanced inputs connected to the respective pulse-shorteners.

15. In the ope-ration of a charged-particle accelerator or the like including a terminal portion .at ra high voltage with respect to its surroundings, the method of producing electrical pulses of vari-able duration and frequency in such terminal portion comprising generating, in -a region substantially spaced from the terminal portion, periodic pulse pairs comprising initiating pulses and terminating .pulses delayed with respect tothe initiating pulses, detecting such pulses in the terminal portion, altering and restoring an electrical parameter in the terminal -portion in response to successive pulses thus detected, and varying the delay between the pulses of the pairs independently of their frequency.

16. Apparatus for charged-particle acceleration .and analogous purposes comprising a high-voltage ltermin-al system insulated from its surroundings, pulse-generating means insulatedly spaced from the terminal system for producing periodic pulse pairs of manually variable time delay, detecting means in the terminal system, and a switch in the terminal system, operable in response to successive pulses so detected to alternate an electrical parameter in the terminal between :two conditions.

References Cited by the Examiner UNITED STATES PATENTS 2,982,917 5/ 1961 Aaland et al 328--229 X JAMES W. LAWRENCE, Primary Examiner.

ARTHUR GAUSS, Examiner.

C. R. CAMPBELL, v. LAFRANCHI,

Assistant Examiners, 

16. APPARATUS FOR CHARGED-PARTICLE ACCELERATION AND ANALOGOUS PURPOSES COMPRISING A HIGH-VOLTAGE TERMINAL SYSTEM INSULATED FROM ITS SURROUNDINGS, PULSE-GENERATING MEANS INSULATEDLY SPACED FROM THE TERMINAL SYSTEM FOR PRODUCING PERIODIC PULSE PAIRS OF MANUALLY VARIABLE TIME DELAY, DETECTING MEANS IN THE TERMINAL SYSTEM, AND A SWITCH IN THE TERMINAL SYSTEM, OPERABLE IN RESPONSE TO SUCCESSIVE PULSES SO DETECTED TO ALTERNATE AN ELECTRICAL PARAMETER IN THE TERMINAL BETWEEN TWO CONDITIONS. 